linux-kernel - Re: [PATCH] fs/proc: add VmTaskSize field to /proc/$$/status

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Date:   Thu, 25 Apr 2019 17:00:43 -0400
From:   Rafael Aquini <aquini@...hat.com>
To:     Joel Savitz <jsavitz@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ram Pai <linuxram@...ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Huang Ying <ying.huang@...el.com>,
        Sandeep Patil <sspatil@...roid.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs/proc: add VmTaskSize field to /proc/$$/status

On Thu, Apr 25, 2019 at 04:57:47PM -0400, Joel Savitz wrote:
> Currently, there is no fast mechanism to get the virtual memory size of
> the current process from userspace. This information is available to the
> user through several means, one being a linear search of the entire address
> space. This is the method used by a component of the libhugetlb kernel
> test, and using the mechanism proposed in this patch, the time complexity
> of that test would be upgraded to constant time from linear time. This is
> especially relevant on 64-bit architechtures where a linear search of
> the address space could take an absurd amount of time. Using this
> mechanism, the modification to the test component would be portable
> across all architechtures.
> 
> Signed-off-by: Joel Savitz <jsavitz@...hat.com>
> ---
>  fs/proc/task_mmu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 92a91e7816d8..f64b9a949624 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -74,7 +74,10 @@ void task_mem(struct seq_file *m, struct mm_struct *mm)
>  	seq_put_decimal_ull_width(m,
>  		    " kB\nVmPTE:\t", mm_pgtables_bytes(mm) >> 10, 8);
>  	SEQ_PUT_DEC(" kB\nVmSwap:\t", swap);
> -	seq_puts(m, " kB\n");
> +	SEQ_PUT_DEC(" kB\nVmSwap:\t", swap);
> +	seq_put_decimal_ull_width(m,
> +		    " kB\nVmTaskSize:\t", TASK_SIZE >> 10, 8);
> +	seq_puts(m, " kB\n");
>  	hugetlb_report_usage(m, mm);
>  }
>  #undef SEQ_PUT_DEC
> -- 
> 2.18.1
> 
Acked-by: Rafael Aquini <aquini@...hat.com>